1. Technical Field
This invention relates generally to electronic image capture devices having auto-focus capabilities, and more particularly to an electronic image capture device that includes an image stability mechanism ensuring that an image is sufficiently stable prior to executing the auto-focus operation.
2. Background Art
Image capture devices, such as digital cameras and other similar mechanisms, are becoming more commonplace. Once available only on high-end professional cameras, today such devices are found in mobile telephones, personal digital assistants, and other portable electronic devices. Two of the more popular image capture technologies are complementary metal oxide semiconductor (CMOS) devices and charge-coupled devices (CCDs). These devices include an image sensor that is configured to measure and quantify incident light. They are small and relatively inexpensive to manufacture, and are thus popular accessories in today's portable electronic devices.
The image capture devices available in many portable electronic devices include an auto-focus feature. Auto-focus systems use image-processing circuits to automatically determine the proper focus, thereby eliminating the need for the user to do so. In most portable electronic devices, the image capture device includes a fixed-focus lens. Without auto-focus capabilities, such a lens is capable of rendering acceptable images from about sixty centimeters to infinity. An auto-focus lens can render highly focused images from ten centimeters to infinity.
While the auto-focus feature increases the range within which properly focused images can be captured, one drawback to such auto-focus mechanisms is that they can be relatively slow. For instance, in some image capture systems integrated into portable electronic devices, the auto-focus system must—through intelligent trial and error—move the lens to a particular position that corresponds to a focused image. The auto-focus system does this by examining an image, moving the lens, capturing another image, and examining it again to determine if the proper focus has been achieved. The process is repeated until the optimal lens position is found. This can take as many as fifteen images. In an image capture device having a 1/15th second frame rate, the entire auto-focus procedure can take one second.
While this may not seem like a large amount of time, the time can be greatly extended where the image capture device is moving and the auto-focus operation is taking place. For instance, a user's shaky hand or a moving platform can cause the image capture device to move significantly. Such movement can result in blurry images, as the autofocus feature lacks a consistent subject upon which to achieve focus. Further, even where focus is finally achieved, such movement cause the auto-focus operation to take even more time to complete.
There is thus a need for an improved image capture device that helps to reduce inefficiencies in auto-focus operations that occur due to image capture device movement.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.